Development of any one field requires corresponding development in other fields. Sometimes the fields are so unrelated that it seems amazing that one field would have influenced the other. But consider the link between diagnostic tests and the observation that the sky is blue. This is not about “blue sky thinking” but rather a direct link in science between the two completely different fields of quantum physics and biological assays.
In many of diagnostic devices the development reagent is usually colloidal gold. This reagent makes the development of a particular color when the test is positive. Usually, it is used as a precipitate of biological antibodies that have been coupled to colloidal gold. When these antibodies cluster or form aggregates, the colloidal gold appears as a colored line in the diagnostic test.
The derivation of this is based on a phenomenon called the Mie effect, that was named after Gustav Mie’s work in the early 20th century. He observed that the colloidal gold formed interesting colored solutions dependent on the size of the colloidal gold particle. The phenomenon of light scattering is dependent on scattering of light by particles. This incidentally is used in other experiments wherein the size of the cells or their aggregates is measured dependent on scattering. The light scattering causes the gold particles to make the solution appear from red to purple.
This same light scattering is responsible for the sky to appear blue since light is scattered to the fourth power of wavelength. Blue light is scattered more than the red light and appears 6 times as bright as the red component thus making the sky look blue.
Thus scattering of light makes the sky looks blue and also develops the color of reagents that are used in diagnostic testing.